I was going to make one from scraps I have on hand but someone said that they were a bad idea because they hold moisture and the wood rots. Would PVC be better? Wouldn't that hold moisture even worse than wood? I just want something so that I can refill it every few days instead of daily, and so I can refill from the top rather than having to turn it upside down and dump all the food in the bowl part.

As long as the feed can't get wet, wood is fine. I've seen hundreds of pictures of wooden feeders and also, growing up here on the farm, most all ours were made of scrap wood.
It will rot someday.... but I've got one my grandfather built back in the 40's that's still in use. We keep all our feeders in the coop in the dry though.

I made wooden wall hanging feeders for grit and oyster shell. Pictures are on "my page", links in my sig.

No wooden feeders are not BAD. You can make use of many materials for feeder wood, metal, plastic, clay, ect. Wood has some advantages as do some of the others. However, do not put an OSB or fiber board wood feeder that will get rained on. Not a good idea.

I built a gravity feeder out of wood that holds about 1/3 of a 50# bag of feed. I have pics of it, but I need to get my computer savy kids to help me get it downloaded on here. It's about 18" wide, about 6" deep, and about 24" tall. I put a piece of plexi-glass in the front of it, so you can see the feed level in it. At the bottom, I angled a piece of wood to direct the feed into the trough at the bottom. There is about a 1" gap that the feed actually goes through. It works perfectly.
I have it mounted on the wall in the run, (not in coop) tucked away in the corner that stays dry no matter how bad it rains. I haven't thought of a winter feeder for inside the coop yet. I think I have a little time.